FI89610C - REFERENCE TO A MECHANICAL REFINING MECHANISM - Google Patents

Description

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METHOD OF MANUFACTURING MECHANICAL GRINDING FROM PULP-BASED RAW MATERIAL

The invention relates to a method for producing a mechanical grit from a cellulosic surface raw material as defined in the preamble of claim 15.

A wide variety of methods for producing a mechanical grinder are already known, in which pre-treated or untreated wood chips are ground in a plate and / or conical grinder in one or several stages. In multi-stage grinding, different grinding blades, different temperatures and pulp consistencies can be used at different stages. Generally, constant speed electric grinders are used, the speed of which depends on the frequency of the electrical network used; A speed of 1500 rpm is commonly used in Europe and a speed of 1800 rpm in North America.

It has been shown that increasing the rotational speeds of a pulp refiner to reduce energy consumption (The Role of Rate of Rotation and Frequency in Refiner Mechanical Pulping, by J. SUNDHOLM, A. HEIKKURINEN and B. MANNSTRÖM .... Paper and Wood 70 (1988): 5, 446-451). The problem in this case is that increasing the rotational speed reduces the quality of the pulp to some extent, especially the tear strength.

The object of the invention is to eliminate the above-mentioned drawback.

In particular, it is an object of the invention to provide a method which provides as good a quality and degree of grinding as conventional grinding methods, but with a clearly lower energy consumption.

The method according to the invention is characterized by what is stated in claim 1.

The invention is based on the basic idea that a cellulosic raw material, such as wood chips, is ground in 2 8961 0 successive stages in several stages. In the first grinding step, the raw material is ground at a higher speed, and in the second grinding step, the raw material is ground at a lower speed than in the first 5 grinding steps. In the first grinding step, the rotational speed of the refiner is preferably set high to achieve a high grinding intensity; in the second grinding step, the rotor speed is adjusted lower to provide a lower grinding intensity.

In one embodiment of the method, in the first grinding step, the refiner speed is greater than 1500 rpm, preferably 1800 to 2400 rpm, and in the second grinding step, the refiner speed is less than or equal to 1500 rpm, preferably 1000 to 1500 rpm.

In one application of the method, in the first grinding step, the temperature of the raw material is adjusted high to soften it. In the second grinding-20 step, the temperature of the raw material is lowered to grind the raw material in a harder state than in the first grinding step. In the first grinding step, the temperature of the steam in the grinder is above 145 ° C, preferably 150 to 170 ° C. In the second grinding step, the temperature of the steam 25 is below 140 ° C, preferably 100-135 ° C.

Grinding can also be carried out in more than two grinding steps. In this case, the temperature of the second stage steam is below 140 ° C, preferably 100 to 135 ° C, most preferably 120 to 135 ° C. In the grinding step following the second grinding step 30, the steam temperature is e.g. 100 to 120 ° C.

In one embodiment of the method, the grinding result of the first grinding step, freeness 200 to 700 ml, preferably 300 to 500 ml, is fractionated into a coarse fraction and a fine fraction. The coarse fraction is preferably ground at a higher intensity than the fine fraction so that the grinding result of the fine fraction

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3 freeness is higher than coarse fraction freeness.

The multi-stage fractionation of the pulp is known per se. The coarse and fine fractions obtained as a result of fractionation are usually ground at the same rotational speed and generally so that the fractions are ground to the same degree of grinding or so that the freeness of the coarser fraction is left higher. In this case, the advantages achieved in the degree of grinding or energy consumption have been small or non-existent. When in one embodiment of the process according to the invention the coarse fraction is ground differently and further, i.e. at a higher speed than the fine fraction, the degree of grinding of the final mass can be obtained as in known fractionation / grinding methods, but the energy consumption is lower. In this way, 15-25% lower energy consumption can be achieved than with conventional methods.

In one embodiment of the invention, method 20 produces fine magazine paper pulp. The coarse fraction is ground, and if desired sorted, to a degree of grinding freeness 20 to 60 ml, preferably 30 to 40 ml, and the fine fraction is ground, and if desired sorted, to a degree of grinding freeness 65 to 120 ml, preferably 70 to 90 ml.

In one embodiment of the method, the speed of the grinding steps is adjusted using grinding blades with different cones. A high grinding speed is achieved with a plate grinder (cone angle 90 °) or with a cone grinder with a large cone angle of 30 °. A lower grinding speed is achieved with a cone refiner with a smaller cone angle.

In one embodiment of the method, with the exception of the first grinding step, other grinding steps use a conical grinder.

The advantage of the invention is that the method can provide as good a pulp quality and a degree of grinding 8 9 610 4 as with conventional grinding methods, but with a clearly, e.g. 10-20%, lower energy consumption.

A further advantage of the invention is that by performing fractionation between grinding and grinding the coarse fraction at a higher speed and beyond the fine fraction, the overall electricity consumption can be reduced by 15-25%.

In the following, the invention will be described by means of two pre-10 characters.

EXAMPLE 1

In one study, the multi-stage pulping process of the invention was compared to a conventional multi-stage hot milling (1500 rpm, 130 ° C). Grinding was performed with a DDC 24 grinder, maximum power 500 kw.

The process according to the invention had a first grinding step in which the raw material was ground at a high rotational speed (2000 rpm) and at a higher than normal temperature (155 ° C). In the grinding steps following the first grinding step, normal rotational speeds (1500 rpm) and lower rotational speeds (1200 rpm) as well as lower than normal temperatures (100-125 ° C) were used.

The results are shown in Table 1.

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Table 1: The quality of the pulp given by the process according to the invention compared to conventional hot rubbing (reference TMP) with a DDC 24 pulverizer.

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Reference Method according to the TMP of the invention

Energy consumption [MWh / t] 2.3 1.9 10 Freeness [ml] 146 130

Minicut [%] 2.8 2.4

Tensile index [Nm / g] 31 30

Tear index [mNmVg] 6.4 6.3

Light scattering coefficient [m2 / kg] 53 53 15

It can be seen from Table 1 that the energy consumption of the process according to the invention was about 17% lower and the quality of the pulp was substantially as good as with the conventional hot grinding process.

20 EXAMPLE 2

In another study carried out with the same equipment, the pulp was prepared using the multi-stage grinding, fractionation and separate grinding of the fractions according to the invention, so that the coarser fraction was ground at a higher speed than the finer fraction. This and the comparative test for conventional hot massage were performed with a different raw material than in Example 1, so the energy consumption / freeness-30 ratio is different.

In this study, the freeness of the pulp after the first grinding step was 660 ml. This mass was fractionated into a coarse fraction (freeness 728 ml) and a fine fraction (freeness 344 ml). Coarser fraction already at 35 rpm, freeness 60 ml and

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Ο finer fraction at 1000 rpm, freeness 120 ml).

The results are shown in Table 2.

Table 2: Interpolated results of the pulp quality of the process according to the invention, which includes fractionation and separate grinding of the fractions, compared to a conventional pre-known lunar rotation (reference TMP)

Reference Method TMP according to the invention 15 Energy consumption [MWh / t] 2.41 2.04

Freeness [ml] 90 90

Tensile index [Nm / g] 39 40

Tear index [mNm2 / g] 6.0 5.9

Light scattering coefficient [m2 / kg] 56 55 20

It can be seen from Table 2 that the energy consumption of the method according to the invention was about 15% lower and the quality of the pulp was substantially as good as with the conventional hot-friction method.

The invention is not limited solely to the application examples presented above, but many modifications are possible while remaining within the scope of the inventive idea defined by the claims.

Claims (11)

8961 0 A method for producing a mechanical pulp from a cellulosic raw material, such as wood chips, in which method the raw material is ground in at least two successive steps, characterized in that in the first grinding step the raw material is ground at a higher speed and temperature and in a second grinding step - 10 the substance is ground at a lower speed and at a lower temperature. Method according to Claim 1, characterized in that in the first grinding step the rotational speed of the refiner is greater than 1500 rpm, preferably 1800 to 2400 rpm. Method according to Claim 1 or 2, characterized in that in the second grinding step the speed of the refiner is less than or equal to 1500 rpm, preferably 1000 to 1500 rpm. Process according to one of Claims 1 to 3, characterized in that the steam temperature of the first grinding step is above 145 ° C, preferably 150 to 170 ° C. Method according to one of Claims 1 to 4, characterized in that the steam temperature of the second grinding step is below 140 ° C, preferably 100 to 135 °. Process according to one of Claims 1 to 5, characterized in that the steam temperature of the second grinding step is from 120 to 135 ° C. Method according to one of Claims 1 to 6, characterized in that the second grinding step is followed by at least one subsequent grinding step, the steam temperature of which is preferably 100 to 120 ° C. Process according to one of Claims 1 to 7, characterized in that the pulp obtained from the first milling step has a freeness of 200 0 B 9 61 G to 700 ml, preferably 300 to 500 ml, are fractionated into a coarse fraction and a fine fraction, and the coarse fraction is ground at a higher intensity than the finer fraction so that the freeness of the ground fine fraction is higher than the freeness of the ground coarse fraction. Method according to one of Claims 1 to 8, characterized in that the method produces fine magazine paper pulp; and that the coarse fraction is ground to a degree of freeness 10 to 60 ml, preferably 30 to 40 ml, and the fine fraction is ground to a degree of freeness 65 to 120 ml, preferably 70 to 90 ml. Method according to one of Claims 1 to 9, characterized in that the latter grinding step is carried out using a conical refiner whose conical angle of the refining blades is lower than that of the refiner used in the previous step. Method according to one of Claims 1 to 10, characterized in that, with the exception of the first grinding step, a conical grinder is used in the grinding steps. i 9 H 9 6 1 0